Showing papers on "Subpixel rendering published in 2005"

A convenient multicamera self-calibration for virtual environments

Abstract: Virtual immersive environments or telepresence setups often consist of multiple cameras that have to be calibrated, We present a convenient method for doing this. The minimum is three cameras, but there is no upper limit. The method is fully automatic and a freely moving bpdght spot is the only calibration object, A set of virtual 3D points is made by waving the bright spot through the working volume. Its projections are found with subpixel precision and verified by a robust RANSAC analysis. The cameras do not have to see all points; only reasonable overlap between camera subgroups is necessary. Projective structures are computed via rank-4 factorization and the Euclidean stratification is done by imposing geometric constraints. This linear estimate initializes a postprocessing computation of nonlinear distortion, which is also fully automatic. We suggest a trick on how to use a very ordinary laser pointer as the calibration object. We show that it is possible to calibrate an immersive virtual environment with 16 cameras in less than 60 minutes reaching about 1/5 pixel reprojection error, The method has been successfully tested on numerous multicamera environments using varying numbers of cameras of varying quality.

A quasi-dense approach to surface reconstruction from uncalibrated images

Abstract: This paper proposes a quasi-dense approach to 3D surface model acquisition from uncalibrated images. First, correspondence information and geometry are computed based on new quasi-dense point features that are resampled subpixel points from a disparity map. The quasi-dense approach gives more robust and accurate geometry estimations than the standard sparse approach. The robustness is measured as the success rate of full automatic geometry estimation with all involved parameters fixed. The accuracy is measured by a fast gauge-free uncertainty estimation algorithm. The quasi-dense approach also works for more largely separated images than the sparse approach, therefore, it requires fewer images for modeling. More importantly, the quasi-dense approach delivers a high density of reconstructed 3D points on which a surface representation can be reconstructed. This fills the gap of insufficiency of the sparse approach for surface reconstruction, essential for modeling and visualization applications. Second, surface reconstruction methods from the given quasi-dense geometry are also developed. The algorithm optimizes new unified functionals integrating both 3D quasi-dense points and 2D image information, including silhouettes. Combining both 3D data and 2D images is more robust than the existing methods using only 2D information or only 3D data. An efficient bounded regularization method is proposed to implement the surface evolution by level-set methods. Its properties are discussed and proven for some cases. As a whole, a complete automatic and practical system of 3D modeling from raw images captured by hand-held cameras to surface representation is proposed. Extensive experiments demonstrate the superior performance of the quasi-dense approach with respect to the standard sparse approach in robustness, accuracy, and applicability.

Sub-pixel Target Mapping from Soft-classified, Remotely Sensed Imagery

Abstract: A simple, efficient algorithm is presented for sub-pixel target mapping from remotely-sensed images. Following an initial random allocation of “soft” pixel proportions to “hard” subpixel binary classes, the algorithm works in a series of iterations, each of which contains three stages. For each pixel, for all sub-pixel locations, a distance-weighted function of neighboring sub-pixels is computed. Then, for each pixel, the sub-pixel representing the target class with the minimum value of the function, and the sub-pixel representing the background with the maximum value of the function are found. Third, these two sub-pixels are swapped if the swap results in an increase in spatial correlation between sub-pixels. The new algorithm predicted accurately when applied to simple simulated and real images. It represents an accessible tool that can be coded and applied readily by remote sensing investigators.

Image registration using log-polar mappings for recovery of large-scale similarity and projective transformations

Abstract: This paper describes a novel technique to recover large similarity transformations (rotation/scale/translation) and moderate perspective deformations among image pairs We introduce a hybrid algorithm that features log-polar mappings and nonlinear least squares optimization The use of log-polar techniques in the spatial domain is introduced as a preprocessing module to recover large scale changes (eg, at least four-fold) and arbitrary rotations Although log-polar techniques are used in the Fourier-Mellin transform to accommodate rotation and scale in the frequency domain, its use in registering images subjected to very large scale changes has not yet been exploited in the spatial domain In this paper, we demonstrate the superior performance of the log-polar transform in featureless image registration in the spatial domain We achieve subpixel accuracy through the use of nonlinear least squares optimization The registration process yields the eight parameters of the perspective transformation that best aligns the two input images Extensive testing was performed on uncalibrated real images and an array of 10,000 image pairs with known transformations derived from the Corel Stock Photo Library of royalty-free photographic images

Video super-resolution using controlled subpixel detector shifts

Abstract: Video cameras must produce images at a reasonable frame-rate and with a reasonable depth of field. These requirements impose fundamental physical limits on the spatial resolution of the image detector. As a result, current cameras produce videos with a very low resolution. The resolution of videos can be computationally enhanced by moving the camera and applying super-resolution reconstruction algorithms. However, a moving camera introduces motion blur, which limits super-resolution quality. We analyze this effect and derive a theoretical result showing that motion blur has a substantial degrading effect on the performance of super-resolution. The conclusion is that, in order to achieve the highest resolution motion blur should be avoided. Motion blur can be minimized by sampling the space-time volume of the video in a specific manner. We have developed a novel camera, called the "jitter camera," that achieves this sampling. By applying an adaptive super-resolution algorithm to the video produced by the jitter camera, we show that resolution can be notably enhanced for stationary or slowly moving objects, while it is improved slightly or left unchanged for objects with fast and complex motions. The end result is a video that has a significantly higher resolution than the captured one.

Super‐resolution mapping of the waterline from remotely sensed data

Abstract: Methods for mapping the waterline at a subpixel scale from a soft image classification of remotely sensed data are evaluated. Unlike approaches based on hard classification, these methods allow the waterline to run through rather than between image pixels and so have the potential to derive accurate and realistic representations of the waterline from imagery with relatively large pixels. The most accurate predictions of waterline location were made from a geostatistical approach applied to the output of a soft classification (RMSE = 2.25 m) which satisfied the standards for mapping at 1 : 5000 scale from imagery with a 20 m spatial resolution.

Color display apparatus

Abstract: A color display apparatus is of the type wherein a unit pixel is constituted by at least three subpixels including first to third subpixels, and at each subpixel, a medium for changing an optical property depending on a voltage applied thereto is disposed. The color display apparatus includes means for applying a voltage, to each of the first to third subpixels, for changing the optical property of the medium within a brightness change range in which light passing through the medium is changed in brightness and a hue change range in which the light passing through the medium assumes chromatic color and a hue of the chromatic color is changed while including combinations of red and green, red and blue, and green and blue for the first to third subpixels, respectively.

Use of multiresolution wavelet feature pyramids for automatic registration of multisensor imagery

Abstract: The problem of image registration, or the alignment of two or more images representing the same scene or object, has to be addressed in various disciplines that employ digital imaging. In the area of remote sensing, just like in medical imaging or computer vision, it is necessary to design robust, fast, and widely applicable algorithms that would allow automatic registration of images generated by various imaging platforms at the same or different times and that would provide subpixel accuracy. One of the main issues that needs to be addressed when developing a registration algorithm is what type of information should be extracted from the images being registered, to be used in the search for the geometric transformation that best aligns them. The main objective of this paper is to evaluate several wavelet pyramids that may be used both for invariant feature extraction and for representing images at multiple spatial resolutions to accelerate registration. We find that the bandpass wavelets obtained from the steerable pyramid due to Simoncelli performs best in terms of accuracy and consistency, while the low-pass wavelets obtained from the same pyramid give the best results in terms of the radius of convergence. Based on these findings, we propose a modification of a gradient-based registration algorithm that has recently been developed for medical data. We test the modified algorithm on several sets of real and synthetic satellite imagery.

Superresolution mapping using a Hopfield neural network with lidar data

Abstract: Superresolution mapping is a set of techniques to obtain a subpixel map from land cover proportion images produced by soft classification. Together with the information from the land cover proportion images, supplementary information at the subpixel level can be used to produce more detailed and accurate land cover maps. This research aims to use the elevation data from light detection and ranging (lidar) as an additional source of information for superresolution mapping using the Hopfield neural network (HNN). A new height function was added to the energy function of the HNN for superresolution mapping. The value of the height function was calculated for each subpixel of a certain class based on the Gaussian distribution. A set of simulated data was used to test the new technique. The results suggest that 0.8-m spatial resolution digital surface models can be combined with optical data at 4-m spatial resolution for superresolution mapping.

An enhanced correlation-based method for stereo correspondence with subpixel accuracy

Abstract: The invariance of the similarity measure in photometric distortions as well as its capability in producing subpixel accuracy are two desired and often required features in most stereo vision applications. In this paper we propose a new correlation-based measure which incorporates both mentioned requirements. Specifically, by using an appropriate interpolation scheme in the candidate windows of the matching image, and using the classical zero mean normalized cross correlation function, we introduce a suitable measure. Although the proposed measure is a nonlinear function of the sub-pixel displacement parameter, its maximization results in a closed form solution, resulting in reduced complexity for its use in matching techniques. Application of the proposed measure in a number of benchmark stereo pair images reveals its superiority over existing correlation-based techniques used for subpixel accuracy.

Machine vision for high-precision volume measurement applied to levitated containerless material processing

Abstract: By combining the best practices in optical dilatometry with numerical methods, a high-speed and high-precision technique has been developed to measure the volume of levitated, containerlessly processed samples with subpixel resolution. Containerless processing provides the ability to study highly reactive materials without the possibility of contamination affecting thermophysical properties. Levitation is a common technique used to isolate a sample as it is being processed. Noncontact optical measurement of thermophysical properties is very important as traditional measuring methods cannot be used. Modern, digitally recorded images require advanced numerical routines to recover the subpixel locations of sample edges and, in turn, produce high-precision measurements.

Method for autostereoscopically producing three-dimensional image information from scanned sub-pixel extracts and device for carrying out said method

Abstract: Known autostereoscopic lensless methods for multiple use in public and private domains by optical grid separation before a matrix screen exhibit serious resolution losses, crosstalk and scan-effects. The inventive multiplex track method (MTV) using a separating raster (TR) obliquely extended with respect to the matrix screen (MB) and an electronic tracking (TS) of viewing arias is based on two separated image views (L, R), adjacently disposes two or three subpixels (SP) of each pixel (P) of the two image views (L, R) in the actual subpixel extraction (SPA), continuously and alternatingly preserving each subpixel address and disposes said subpixels (SP) in an overlapping manner on each other with an offset, thereby the resolution loss effects the subpixels (SP), only. The crosstalk resulting from the inclination of the separation raster (TR) is reduced by a special structure of the subpixel extraction (SPA), wherein the resolution homogenisation in two direction of the screen is simultaneously preserved. The formation of the actual subpixel extraction (SPA) Is carried out according to multiplex schemes (MUXi) predetermined according to an observer actual position. One or several observers can be electronically tracked subject to the distance thereof from a conventional matrix screen (MB) and the image representation can be adapted therefor.

Method and system for fast implementation of subpixel interpolation

Abstract: A subpixel interpolator includes an input memory capable of storing video information formed from full pixels. The subpixel interpolator also includes at least one interpolation unit capable of performing subpixel interpolation to generate half-pixels and quarter-pixels in parallel. Multiple half-pixels and multiple quarter-pixels are generated concurrently during the subpixel interpolation. In addition, the subpixel interpolator includes an output memory capable of storing at least some of the full pixels, half-pixels, and quarter-pixels. In some embodiments, the at least one interpolation unit includes a horizontal half-pixel interpolation unit, two vertical half-pixel interpolation units, and a quarter-pixel interpolation unit, all of which may operate in parallel. In particular embodiments, the interpolation units are formed from adders and shifters and do not include any multipliers.

Fast and subpixel precise blob detection and attribution

Abstract: This paper introduces an algorithm for fast and subpixel precise detection of small, compact image primitives ("blobs"). The algorithm is based on differential geometry and incorporates a complete scale-space description. Hence, blobs of arbitrary size can be extracted by just adjusting the scale parameter. In addition to center point and boundary of a blob, also a number of attributes are extracted. These describe the specific blob characteristics in more detail and, thus, allow for a subsequent classification of blobs. Several examples on real images illustrate the performance of the proposed algorithm.

Three-dimensional display

Abstract: An object of the present invention is to eliminate color non-uniformity and intensity non-uniformity on a three-dimensional image The present invention provides a three-dimensional display comprising: a two-dimensional display, which comprises a plurality of color subpixels arranged in rows extending in a horizontal direction and in columns extending in a vertical direction which is substantially perpendicular to the horizontal direction, the color subpixels of red, green and blue being arranged periodically in the rows and the color subpixels of the same color being arranged in the columns; and a lenticular sheet provided on the two-dimensional display and having a plurality of cylindrical lenses through which the color subpixels are viewed and which extend in parallel with one another, the central axis of each cylindrical lens being inclined at an angle of θ to the column of the two-dimensional display, wherein, when a pitch of the color subpixels in the horizontal direction is p x , a pitch of the color subpixels in the vertical direction is p y , and a color subpixel group constituting one three-dimensional pixel is constituted by 3M×N number of color subpixels where 3M is the number of color subpixels in each row of one of the cylindrical lenses and N is the number of color subpixels in each column of one of the cylindrical lenses, a relationship, θ=tan −1 (3p x /NP y ), is satisfied

Theoretical and experimental assessment of noise effects on least-squares spectral unmixing of hyperspectral images

Abstract: The problem of input noise affecting the subpixel classifica- tion is examined in order to assess its relationship with the output noise The approach followed in this study was to investigate the output noise level obtained with a least-squares subpixel classification algorithm ap- plied to simulated spectra The simulation of mixed pixel spectra took into account variable pixel composition and a selectable power of the superimposed noise Noise was considered a zero-mean stochastic pro- cess over wavelength that was assumed to be jointly normal and uncor- related The paper outlines the structure and the mathematical proper- ties of the performed unmixing simulations, and clearly shows the relationship between input and output noise It is shown that a simple exponential law relates with substantial accuracy the standard deviation of input noise to that of the computed subpixel abundances for fully constrained unmixing As expected, the cases of unconstrained and abundances sum to one partially constrained unmixing are controlled by a linear relationship between input and output noise amplitude The paper also shows the dependence of unmixed abundances and output noise on the spectral similarity of end members involved in the unmixing Three subpixel classification approaches unconstrained, partially con- strained, and fully constrained algorithms were investigated © 2005 Soci-

Correction method and software for image distortion and nonuniform response in charge-coupled device-based X-ray detectors utilizing X-ray image intensifier

Abstract: An on-site method of correcting the image distortion and nonuniform response of a charge-coupled device (CCD)-based X-ray detector was developed using the response of the imaging plate as a reference. The CCD-based X-ray detector consists of a beryllium-windowed X-ray image intensifier (Be-XRII) and a CCD as the image sensor. An image distortion of 29% was improved to less than 1% after the correction. In the correction of nonuniform response due to image distortion, subpixel approximation was performed for the redistribution of pixel values. The optimal number of subpixels was also discussed. In an experiment with polystyrene (PS) latex, it was verified that the correction of both image distortion and nonuniform response worked properly. The correction for the "contrast reduction" problem was also demonstrated for an isotropic X-ray scattering pattern from the PS latex.

Performance Analysis and Validation of a Stereo Vision System

Abstract: This paper presents an in-depth performance analysis and validation of a correlation based stereo vision system being used as part of the ongoing 2003 Mars Exploration Rover flight mission. Our analysis includes the effects of correlation window size, pyramidal image down-sampling, vertical misalignment, focus, maximum disparity, stereo baseline, and range ripples. A key element of validation is to determine the stereo localization error both analytically and experimentally. We study both down-range and cross-range error and verify that while camera calibration inaccuracy contributes to both, stereo correlation error affects only the former. Error contributions of subpixel interpolation, vertical misalignment, and foreshortening on stereo correlation are examined carefully. A novel method using bricks with reflective metrology targets and a mast-mounted stereo camera system enabled experimental measurements of the stereo disparity error. The standard deviation of the down-range disparity error was measured at sigma=0.32 pixel for high-resolution 1024times768 camera images. The result is critical in evaluating accurate rover navigation and instrument placement within given error budgets

System and method for improving sub-pixel rendering of imaging data in non-striped display systems

Abstract: The present application discloses a number of embodiments for the mapping of input image data onto display panels in which the subpixel data format being input may differ from the subpixel data format suitable for the display panel. Systems and methods are disclosed to map input image data onto panels with different ordering of subpixel data that the input, different number of subpixel data sets or different number of color primaries that the input image data.

Identification of translational displacements between N-dimensional data sets using the high-order SVD and phase correlation

Abstract: This paper presents an extension of the phase correlation image alignment method to N-dimensional data sets. By the Fourier shift theorem, the motion model for translational shifts between N-dimensional images can be represented as a rank-one tensor. Through use of a high-order singular value decomposition, the phase correlation between two N-dimensional data sets can be decomposed to independently identify translational displacements along each dimension with subpixel resolution. Using three-dimensional MRI data sets, we demonstrate the effectiveness of this approach relative to other N-dimensional image registration methods.

Subpixel routing and processing for an imaging system or the like

Abstract: Count rates may be obtained from one or more subpixels for a given pixel in an imaging system detector. Count rates may be obtained from individual subpixels, or may be from electronically binned subpixels at least in part in various subpixel arrangements where a selected subpixel arrangement may be adaptively set according to a detected count rate. For lower count rates, two or more subpixels may be electronically binned together and the counts may be obtained from the binned subpixels, for example to mitigate a charge sharing effect. For higher count rates, the count rates of a greater number of subpixels may be individually obtained, for example to mitigate a pulse pile-up effect. Detective quantum efficiency may be optimized over a wider range of photon flux rate via the adaptive subpixel arrangement.

Color lcd with bi-color sequential backlight

Abstract: In an LCD, a backlight (32) having red, green, and blue LEDs is controlled to generate monochromatic light (e.g., blue) during a portion of a cycle, such as an image frame cycle. During another portion of the cycle, all the LEDs are illuminated to create white light. The color filter in the LCD panel contains, for each white pixel, a first color (e.g., red) subpixel filter (42), a second color (e.g., green) subpixel filter (43), and a clear subpixel area (44) for passing white light and the monochromatic. The liquid crystal layer shutters are controlled to pass from 0-100% of the light for their associated subpixels to create a color image. With proper control of the shutters, any desired color of each white pixel can be achieved during the cycle. By converting one color filter to a clear area, the transmission efficiency of the display is greatly increased.

Graphical processing system, graphical pipeline and method for implementing subpixel shifting to anti-alias texture

Abstract: A system, apparatus, and method are disclosed for modifying positions of sample positions for selectably oversampling pixels to anti-alias non-geometric portions of computer-generated images, such as texture, at least in part, by shifting shading sample positions relative to a frame of reference. There is generally no relative motion between the geometries and the coverage sample positions. In one embodiment, an apparatus, such as a graphics pipeline and/or a general purpose graphics processing unit, anti-aliases geometries of a computer-generated object. The apparatus includes at least a texture unit and a pipeline front end unit to determine geometry coverage and a subpixel shifter to shift shading sample positions relative to the frame of reference. The apparatus can receive subpixel shifting masks to select subsets of shading sample positions. Each of the shading sample positions is shifted to a coverage sample position to reduce level of detail (“LOD”) artifacts.

Dropout control in subpixel rendering

Abstract: The present invention relates to dropout control in which one or more samples are added to adjacent samples that fall within an image outline. The samples are used in sub-pixel rendering to compensate for unnaturally thin or faint object stems. Horizontal dropout control operations are provided to add samples to sets of horizontally adjacent samples such that each set of samples comprises a minimum number of samples. Vertical dropout control operations are provided to position samples such that the weighted anti-aliasing filtering will take sufficient account of the samples. In one embodiment, an associative table is utilized to calculate alternative patterns of samples. In another embodiment, the baseline of an object is used in the dropout control operations to reduce artifacts that can be created by the addition of samples in the vertical direction.

Inferring motion from the rank constraint of the phase matrix

Abstract: We investigate the rank constraint of the discrete phase difference, and derive its exact parametric model. We show that the discrete phase difference of two shifted images, or their subregions, is a 2-dimensional sawtooth signal. This allows us to determine the motion parameters to subpixel accuracy by simply counting the number of cycles of the phase difference along each frequency axis. The subpixel portion is given by the non-integer fraction of the last cycle along each axis. The problem is formulated as a homogeneous cost function under rank constraint for the phase matrix, and the shape constraint for the filter that computes the group delay, and is solved using a robust technique.

Extended object wavefront sensing based on the correlation spectrum phase

Abstract: In this paper we investigate the performance of a Fourier based algorithm for fast subpixel shift determination of two mutually shifted images subjected to noise. The algorithm will be used for Shack-Hartmann based adaptive optics correction of images of an extended object subjected to dynamical atmospheric fluctuations. The performance of the algorithm is investigated both analytically and by Monte Carlo simulations. Good agreement is achieved in relation to how the precision of the shift estimate depends on image parameters such as contrast, photon counts and readout noise, as well as the dependence on sampling format, zero-padding and field of view. Compared to the conventional method for extended object wavefront sensing, a reduction of the computational cost is gained at a marginal expense of precision.

Image display apparatus

Abstract: PROBLEM TO BE SOLVED: To provide an image display apparatus in which high resolution display with a low cost is realized without increasing the number of pixel units and in which high quality image without flicker is displayed SOLUTION: The apparatus is equipped with a plurality of pixel units 2 having a light emitting means 4 capable of coloring any color and a light control means 7 which is mounted on a display side of the pixel unit 2 and which has a plurality of subpixels 8 being smaller than each display area of the pixel unit 2 and which controls a transmitted amount of coloring light emitted from the light emitting means 4 for each subpixel 8 As human eyes are more sensitive to brightness change than to color change, it is felt that display quality is improved by enhancing a brightness resolution and thus display resolution of the image display apparatus is enhanced The light control means 7 may be mounted on each pixel unit 2 or on each group of the plurality of pixel units The plurality of pixel units 2 may be arranged in a row-column two dimensional matrix state and a liquid crystal display cell can be used for the light control means 7 COPYRIGHT: (C)2005,JPO&NCIPI

Super resolution: an overview

Abstract: : Super-resolution algorithms produce a single high-resolution image from a set of several, low-resolution images of the desired scene. The low-resolution frames are shifted differently with respect to the high resolution frame with subpixel increments. This paper presents first a theoretical overview of super-resolution algorithms. The most important methods, namely, the iterative back-projection, projection onto convex sets, and maximum a posteriori estimation are then compared within the same framework of implementation.